The invention relates to a scanning device for optically scanning a surface along a line, which device comprises a radiation-sensitive detection system for detecting radiation originating from the surface, and further an optical system for imaging an area of the surface on the radiation-sensitive detection system and a deflection system for selecting said area of the surface to be scanned, said optical system comprising a first and a second cylindrical sub-system, the first cylindrical sub-system being arranged proximate and parallel to the line to be scanned and the second cylindrical sub-system being arranged proximate to the detection system. A device of this type is used for inspecting the surface of an object, for example for reading marks which are present on this object. Such a device is also used for inspecting products such as an electronic circuit to check whether the components arranged on this circuit are present in their correct positions.
A device of the type described in the opening paragraph is known from U.S. Pat. No. 3,787,107. This Patent describes a device with which the surface of an object which is present on a conveyor belt is scanned for reading the information in the form of marks such as letters provided on the object. A line on the surface is scanned by means of a light spot, using a laser beam and a deflection system in the form of a rotating polygon mirror. The presence of the light spot selects areas of the line. The radiation reflected by the surface is subsequently projected on a photo-electric converter via two cylindrical systems in the form of cylindrical lenses. The output signal of the photo-electric converter, or the radiation-sensitive detection system is a measure of the reflection coefficient of the surface and hence of the presence or absence of a mark.
The known device measures the quantity of radiation, and hence the reflection coefficient, of the area on the surface which is illuminated by the radiation beam. However, the known device is not suitable for performing other measurements, notably for determining the relief of the surface by measuring the profile along the line to be scanned. Such a profile measurement is particularly advantageous when inspecting articles having a surface varying in height such as, for example an electric circuit whose components must be arranged in fixed positions on a flat supporting plate, or marks which are distinguished from their background in height but not in colour.